The proposal presented here is divided into two parts: the first contains my proposed career plan and the second describes the research strategy for the proposed project. My interest in vascular biology research began with my first clinical encounters with patients suffering from idiopathic pulmonary hypertension (IPAH). Interest in the pathobiology of the disease led me to continue training as a pulmonologist at the University of Colorado but, due to family related reasons, I moved from Denver to Stanford University after my first year of fellowship to continue my research training under the mentorship of Dr. Marlene Rabinovitch, a leader in the field of vascular research. Over the last four years, I have completed two projects dealing with the interaction between Wingless (Wnt) and bone morphogenetic protein (BMP) signaling in pulmonary artery endothelial (PAEC) and smooth muscle cells. Furthermore, during the same time period, I have been awarded both a K12 and, a Harold Amos career development award to continue my current career track as a physician scientist. Since the initial submission, I have become an assistant professor of medicine at Stanford University, a position that allows me to devote 80% of my time to activities related to my research project such as participating in scientific conferences, learning new experimental techniques and methods of data analysis and presenting progress reports of my research to my advisors and peers. In addition to regular one-on-one meetings with my mentor Dr. Rabinovitch, I will meet quarterly with a panel of advisors and consultants that will provide criticism and help discuss ideas related to the proposed research. In an effort to keep abreast of the latest ideas in my field of research, I will enroll in a series of graduate courses in biology, genetics and biostatistics taught by Stanford University faculty and learn the basic principles for responsible conduct in research. Finally, the remainder of my time (20%) will be spent in teaching activities aimed at training residents and fellows in the management of PAH patients in both inpatient and outpatient settings. My long term goals are to have sufficient published and preliminary data to support my independence as an investigator and to submit an R01 grant that will focus on applying the data obtained in these proposed studies to investigating how abnormal Wnt signaling may contribute to IPAH development. The second part of the proposal contains the research plan. IPAH is a rare and progressive disorder associated with abnormally elevated pulmonary pressures that, if untreated, lead to congestive heart failure and premature death. Patients with PAH demonstrate progressive narrowing and loss of small distal pulmonary arteries without significant compensatory vascular regeneration indicating that a defect in pulmonary angiogenesis is present. Recent studies by our group and others have shown that mutations in the bone morphogenetic protein receptor (BMPR) II could contribute to vessel loss by reducing pulmonary artery endothelial cell (PAEC) survival and proliferation in response to injury but the mechanisms by which BMPRI can regulate these angiogenic responses have not been well characterized. In addition to PAECs, pericyte recruitment is critical for stabilization o newly formed vessels but their contribution to the pathogenesis of IPAH has not been well established. We have recently shown that BMP signaling promotes pulmonary angiogenesis by recruitment of two Wnt signaling pathways in PAECs: the canonical Wnt/?-catenin (? C) and the non-canonical Wnt/planar cell polarity (PCP) pathways. Based on our preliminary studies and our review of the literature, we propose that activation of the Wnt/PCP pathway is required for pulmonary angiogenesis by 1) inducing PAEC to organize into properly aligned vascular tubes and 2) by promoting pericyte recruitment to vascular tubes to form functional blood vessels. In a series of experiments using PAECs and pericytes obtained from the lungs of healthy donors and IPAH patients, we will demonstrate that Wnt/PCP signaling is required to direct PAEC (Aim 1) and pericyte (Aim 2) behavior during angiogenesis and that loss of activity correlates with reduced pulmonary angiogenesis. Furthermore, we will complement these cell studies with work on two animal models of dysfunctional Wnt/PCP signaling that will help provide insight into the biological relevance of this pathway to compensatory angiogenesis following pneumonectomy (Aim 3). Future studies will center on how mutations that reduce Wnt/PCP signaling can genetically interact with BMPRII mutations to promote development of IPAH and how therapeutic interventions aimed at normalizing Wnt/PCP pathway activity in PAEC and pericytes could help prevent progression and improve survival in IPAH patients by restoring their ability to regenerate lost vessels.